Swapped the Slide Stop Lever from my Glock 43 into my SS80. Same issue. I did notice that IF the trigger pin is NOT all the way in and the Slide Stop Lever is NOT in the grove of the trigger pin, the Slide Stop Lever does not have the free play that is causing the issue.
Glock 43 on the left and SS80 on the right.
Glock 43
SS80
Gary